Insufficient sleep has been linked to adverse metabolic changes and increased risk of chronic disease including obesity, type 2 diabetes mellitus and early mortality. With age, most Americans increase visceral adiposity and become more likely to develop diabetes. Chronic insufficient sleep associated with 'normal aging' may be one of the factors involved in contributing to metabolic aging'. Physiological changes in metabolism due to sleep loss for 1-2 weeks in young and middle-aged adults include reduced insulin sensitivity and hormonal changes that would increase the likelihood of obesity and diabetes in the long term. Our current data demonstrate that metabolic dysfunction occurs in young and older adults exposed to the combination of chronic sleep loss and recurrent circadian disruption for 3 weeks. Yet sleep loss experiments lengthen photoperiod, introducing a potential confounding effect on circadian rhythmicity, and circadian disruption itself has been shown to lead to adverse metabolic changes. Thus, the effects of sleep loss (with minimal circadian disruption) on glucose metabolism in older adults are not known. In Project 2, we will examine the metabolic responses to 3 weeks of sleep loss in a protocol with minimal circadian disruption to test the hypothesis that older adults will exhibit progressive decrements in total body and adipose tissue insulin sensitivity. We will determine the extent of the changes (glycemic responses to standardized meals, insulin sensitivity via euglycemic hyperinsulinemic clamps), the mechanisms of changes (via adipose tissue biopsy, sympathetic activation, and glucocorticoid activation) and the dynamics of changes (distinguishing effects over a few days and chronic effects over 3 weeks). Moreover, we hypothesize older adults will exhibit recovery of metabolic function with 1 week of sleep recovery. This Project will contribute to understanding the mechanisms by which sleep loss impairs metabolism in older adults, contributing to future research to reduce the risk of diabetes, improve existing therapies, and enhance the health and quality of life of older Americans whose sleep is insufficient.